1. Field of the Invention
The present invention relates to a display device including an oxide semiconductor.
2. Description of the Related Art
In recent years, a technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. The transistors are applied to a wide range of electronic devices such as ICs or electro-optical devices, and there is an expectation for immediate development of especially transistors to be used as switching elements for image display devices. Various metal oxides are used for a variety of applications. Indium oxide is a well-known material and is used as a transparent electrode material which is necessary for liquid crystal displays and the like.
Some metal oxides have semiconductor characteristics. Examples of such metal oxides having semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like. Transistors in which a channel formation region is formed using such metal oxides having semiconductor characteristics are known (Patent Documents 1 and 2).
Furthermore, the transistors including oxide semiconductors have relatively high field-effect mobility. Thus, with use of the transistors, a driver circuit in a display device or the like can be formed.